I am sorry for your loss. Was an estate opened? Did you get an EIN for the estate (or trust if he had one)?
Hopefully, you have access to his mail. Regardless, there is little choice other than to wait as the IRS still has a backlog and returns filed by decedents (or on their behalf) simply take longer to process.
I am aware of several personal representatives who filed for refunds on behalf of decedents who passed away in 2019 and the refunds have yet to be received.
